The overall objective of the proposed research is to correlate histological and chemical changes in the brain with changes in the computerized axial tomogram (CT scan), and to define an effective means for quantitatively measuring cerebral edema in the living subject. On the experimental side, this will be pursued by correlating changes in the attenuation numbers in the CT scan of the rhesus monkey, obtained from an EMI head scanner, following the production of cryogenic cerebral lesions, with changes in water, electrolytes, and plasma protein in the brain. In the human, this will be pursued by correlating histologic changes in the brain obtained at autopsy, with the attenuation numbers in the CT scan obtained shortly before death. We shall also attempt to measure the attenuation numbers of lipids, proteins, and electrolytes in solution by means of a phantom placed in the head unit of the EMI scanner. These figures will then be correlated with measured changes in the human CT scan seen with lesions associated with cerebral edema.